Device to suppress high frequency oscillations



Jan. 31, 1939. c. s. NICOUD ET AL 1' 2,145,629

DEVICE TO SUPPRESS HIGH FREQUENCY OSCILLATIONS Filed May 26, 1937 Im/entors. I (area/[as 5. fV/aazm fizz Ward r/ ,fltta'ae Patented Jan. 31, 1939 v UNITED STATES PATENT OFFICE Cornelius S. Nicoud and Edward J. Wiggins, Ohicage, 11].; said Nlcoud assignontosald Application May 26, 1987, Serial No. 144,912

lclaim.

The invention relates generally to a device for eliminating the eifect on radio circuits of sparking and more particularly to the construction and assembly of such a device for suppressing the production of high frequency oscillations caused by sparking in the usual electric circuits of a motor vehicle, or the like, which seriously interferes with reception of a radio receiving apparatus mounted on said vehicle.

In the use of radio apparatus mounted by motor vehicles the useful transient oscillations of fundamental frequency produced in the ignition system causes no material interference with the proper operation of the radio apparatus but transient oscillations of comparatively much higher frequency caused by arcing or sparking of various electrical devices in the various electrical circuits of the vehicle seriously impair and destroy the reception of the radio apparatus. An object of the invention is to provide novelly constructed resistance elements having suitable low capacity and inductance adapted to be arranged in series with the spark producing elements of the ignition system for effectively suppressing the transient oscillations of high frequency heretofore referred to.

Another object is to provide resistance elements of the character described with separable resistance units.

Another object is to provide an article of the character referred to wherein the resistance units are completely encased and protected from breakage or efilciency impairment by oil or other foreign matter.

Another object is to provide a resistance unit adapted for the use herein which is novel in construction, easy and inexpensive to assemble and manufacture, easy to install, and eflicient in operation.

9 The foregoing and such other objects of the invention as will appear hereinafter as the description proceeds will be more readily understood from a perusal of the following specification; reference being had to the accompanying drawing, in which:

Fig. 1 is a diagrammatic view showing the relative arrangement of a radio apparatus and various parts of an automobile ignition system embodying features of the invention.

Fig. 2 is a longitudinal sectional view of one of the resistance elements embodying the invention.

Fig. 3 is a longitudinal sectional view through 5 another type of resistance element.

Fig. 4 is a longitudinal sectional view through the improved resistance unit.

As illustrated in Fig. 1 a radio receiver apparatus ll preferably is mounted in the customary manner upon the instrument board I! of a motor 5 vehicle to aiford operation thereof by providing ready access to its various controls. Although the circuit of the'radio receiver apparatus is independent of the ignition and other circuits in the vehicle the position of mounting of the radio 10 receiving apparatus necessarily places it in close proximity with such electrical circuits thus giving rise to the electro-magnetic relation therebetween.

The conventional ignition system illustrated l5 usually includes a battery II, a generator l4, spark coil l5, distributor l6, and spark plugs I1, suitably connected by various leads whereby a spark gap discharge is eifected in the various spark plugs at regular timed intervals through 20 operation of the distributor l8.

It is readily apparent that the radio receiving apparatus II which is highly sensitive to static interference, necessarily must be distributed in operation by normally existing extremely high 25 frequency oscillations of the order of ten thousand kilocycles arising in the ignition or other circuits from such incidents as sparking at the commutator brushes of the generator ll, sparking at the contacts of the distributor l8, and 30 spark discharges at the spark plugs II. To overcome this interference it is necessary that the radio receiving apparatus be specially protected and to this end various condensers of high capacity value have been connected in series with 35 the spark producing elements causing such objectionable oscillations. In other instances a resistance unit of high resistance material such as a graphite rod, has been connected one in series with each spark plug to make the paths normally directing the flow of high frequency oscillations caused by sparking in said circuits, to be substantially completely suppressed.

The latter method, although being satisfactory from the standpoint of substantial suppression, is highly susceptible of breakage because of constant vibration of the vehicle and carelessness. The efllciency of such units often becomes impaired because of accumulation of dirt, grit and grease thereon which serves as a by-pass for the oscilla- 5o tions.

The improved element for suppressing the high frequency oscillations is constructed to insure against breakage and fully protect the resistance unit therein, thus resulting in highly efflcient 5 metallic plug 2! having a terminal post 22 extending therefrom to which is attached the circuit cable 23 of one spark plug. The metallic end cap 24 on one end of the unit 20 is held in electrical contact with plug 2| by a spring 25 which is interposed between a metallic end cap 26, on the other end of unit 20, and a metallic plug 21 closing the other end of housing l3. This plug also has a terminal extension 23 which extends through an aperture in and riveted over one arm 28 of a substantially U-shaped bracket 3! for mechanically and electrically securing the plug 21 and bracket together. The other arm 32 of said bracket also is apertured for mounting on the terminal post 33 of spark plug l'l.

As shown the unit 20 comprises metallic end caps 24 and 26 embracing the ends of and in electrical connection with a resistance coil 34 preferably having a value of 12,500 ohms resistance. A resistance unit having such a high resistance is suitable for all general use under various conditions and possesses substantially no inductance and very little distributed capacity, thus it will not impair operation of the ignition system as its capacity is small compared to that of the spark gaps 35 at the spark plug. This added resistance merely dampens the high frequency oscillations heretofore referred to.

Referring particularly to Fig. 4 the unit 20 preferably consists of a hollow core 36 having a layer of wire thereon forming coil 34. It has been found that most eflicient results have been obtained by the use of enamel covered resistance wire closely wound along the entire length of the core 36. After the coil is wound it preferably is coated with shellac 31, or other suitable binder which is not effected by moisture or heat and does not dissolve the enamel on the wire, to retain the coils in place. The end caps 24-46 then are fitted over the ends of the wire covered core and electrical contact therebetween is insured by placing the assembled coil in a suitable instrument which punches projections 38 in the caps thus making one or more points of contact with the wire-said projections piercing the insulation coating 31 and the enamel on the wire without breaking the wire. When the coil is placed in use the points of contact become welded to the wire and insure permanent contact.

Under certain conditions where interfering high frequency oscillations are set up in that part of the circuit connecting the spark coil II and the distributor l3 usually because of the length of the lead 33 therebetween, it is desirable and often necessary to insert a resistance element in said lead to dampen the oscillations. To this end the element 4| is substantially like the one previously described including housing I and resistor unit 20. The unit 23 is confined in the housing by tightly fitting metallic plugs 42 and preferably is held in electrical contact with said plugs by compression spring 25. As shown each end plug 42 preferably is cup-shaped and has a centrally located screw 42 extending outwardly therefrom for electrical engagement with the uninsulated ends of the conductor in lead 33 which is split to receive the resistance unit in series therewith. The combined resistance of the two units l8 and 4| is sufficient to suppress the undesirable osciilations without impairing the efficient operation of the ignition system.

Although applicants are aware that certain steps have been taken to substantially suppress transient oscillations of high frequency interfering to the operation of a radio apparatus they claim as their invention the new and improved means for accomplishing this result in a highly satisfactory manner and the arrangement of such novel means in a novelly constructed mounting element to insure maximum efllciency and adequate protection.

We claim:

In an electric ignition system for an internal combustion engine having spark plugs normally causing oscillations disturbing to radio apparatus, means for substantially eliminating such disturbing oscillations connected in series with the circuit of each spark plug comprising, in combination, a tubular housing of insulation material, conductors extending into and closing the open ends of said housing, one of said conductors being connected to the spark plug cable and the other carrying a substantially U-shaped bracket for mounting directly on the terminal of said spark plug, a coil of insulated wire mounted in said housing, a coating of insulation on said coil, a metallic cap on each end of said coil, detents in said caps electrically connecting said caps to said coil, and a spring in said housing between one end of said assembled coil and one of said conductors, said spring urging the cap on the other end of said coil tightly against the other conductor to complete an electrical connection between the cable and spark plug.

CORNELIUS S. NICOUD. EDWARD J. WIGGINS. 

